There are those who say the climate has always changed, and that carbon dioxide levels have always fluctuated. That’s true. But it’s also true that since the industrial revolution, CO₂ levels in the atmosphere have climbed to levels that are unprecedented over hundreds of millennia.

So here’s a short video we made, to put recent climate change and carbon dioxide emissions into the context of the past 800,000 years.

The temperature-CO₂ connection

Earth has a natural greenhouse effect, and it is really important. Without it, the average temperature on the surface of the planet would be about -18℃ and human life would not exist. Carbon dioxide (CO₂) is one of the gases in our atmosphere that traps heat and makes the planet habitable.

Modern scientists and engineers have explored these links in intricate detail in recent decades, by drilling into the ice sheets that cover Antarctica and Greenland. Thousands of years of snow have compressed into thick slabs of ice. The resulting ice cores can be more than 3km long and extend back a staggering 800,000 years.

Antarctic temperature changes across the ice ages were very similar to globally-averaged temperatures, except that ice age temperature changes over Antarctica were roughly twice that of the global average. Scientists refer to this as polar amplification (data from Parrenin et al. 2013; Snyder et al. 2016; Bereiter et al. 2015).Ben Henley and Nerilie Abram

In previous warm periods, it was not a CO₂ spike that kickstarted the warming, but small and predictable wobbles in Earth’s rotation and orbit around the Sun. CO₂ played a big role as a natural amplifier of the small climate shifts initiated by these wobbles. As the planet began to cool, more CO₂ dissolved into the oceans, reducing the greenhouse effect and causing more cooling. Similarly, CO₂ was released from the oceans to the atmosphere when the planet warmed, driving further warming.

But things are very different this time around. Humans are responsible for adding huge quantities of extra CO₂ to the atmosphere – and fast.

Before the industrial revolution, the natural level of atmospheric CO₂ during warm interglacials was around 280 ppm. The frigid ice ages, which caused kilometre-thick ice sheets to build up over much of North America and Eurasia, had CO₂ levels of around 180 ppm.

Burning fossil fuels, such as coal, oil and gas, takes ancient carbon that was locked within the Earth and puts it into the atmosphere as CO₂. Since the industrial revolution humans have burned an enormous amount of fossil fuel, causing atmospheric CO₂ and other greenhouse gases to skyrocket.

In mid-2017, atmospheric CO₂ now stands at 409 ppm. This is completely unprecedented in the past 800,000 years.

The fundamental science is very well understood. The evidence that climate change is happening is abundant and clear. The difficult part is: what do we do next? More than ever, we need strong, cooperative and accountable leadership from politicians of all nations. Only then will we avoid the worst of climate change and adapt to the impacts we can’t halt.